The present invention relates to passive infrared motion detectors of the type used in outdoor lighting fixtures to illuminate an area such as a walkway or driveway when a person or automobile approaches. The invention is more particularly directed to amplification and filtering circuitry for reducing false activations.
Outdoor motion-activated lighting fixtures are found in widespread use to monitor and illuminate areas around houses, other buildings, walkways, driveways, garden areas, gateways or other areas subject to pedestrian traffic. These lighting fixtures commonly include a passive infra-red (PIR) motion detector that operates by sensing changes in infra-red energy from the region monitored by the motion detector. The motion detector defines a plurality of sensitive detection zones interspersed with dead zones in the monitored region. Infra-red energy from the detection zones is focused onto one or more sensors while infra-red energy from the dead zones it not. As a person moves about within the region into and out of detection zones and neighboring dead zones, the amount of infra-red energy directed to one of the sensors from the detection zone will change, thereby triggering the light to go on.
PIR motion detectors are subject to false activation, that is, activation from infra-red energy changes that are caused by something other than movement of an intended target. Outdoor PIR motion detectors are susceptible in particular to false activations from environmental factors. Localized thermal imbalances and gentle air disturbances can produce localized transport of infra-red energy that is imperceptible or nearly imperceptible to casual human observation, yet that may traverse the boundary of a detection zone and trigger a false activation. Known PIR motion detectors have employed a number of methods to eliminate false activations, which nevertheless continue to occur.